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UREA                                      I27

and froth up. When it fuses quietly, the dark coloured liquid
mass is poured on to an iron pl.tie and allowed to cool.
It solidifies and is powdered and separated from the solid
cake of metallic lead. 200 c.c. of cold water are poured on
to the crude cyanate and, after standing- an hour, filtered
through a fluted filter and washed with a little cold water.
A concentrated solution of 25 grains of ammonium sulphate
is immediately added to the filtrate, which is evaporated to
dryncss on the water-bath, the mass being stirred occa-
sionally to prevent the formation of a surface crust. The
cooled residue is powdered and the urea extracted with alcohol
by boiling on the water-bath, using a reilux condenser and
adding successively small quantities of spirit until the extract
leaves only a small residue on evaporation on a watch-glass.
The greater part of the alcohol is distilled off on the water-
bath, and the residue poured out into a beaker to crystallise.
Yield about 15 grams.

1.              4KCN + Pb,,04 = 4CONK + 3Pb

2.  (NH4)3SO,i + 2CONK - 2CON.NH4 + K>SO4

3.                      CO N. N H4 = C0( N H2)sj

Properties.  Colourless prisms ; in. p. 132; very soluble in
water ; soluble in hot alcohol.

Reactions.  r. Add to a strong solution of urea in water a
drop of concentrated nitric acid, and to another portion a
concentrated solution of oxalic acid ; the crystalline nitrate
CO(NH3)2HNO., and oxalate (.CO(NH2)2)2CaHaO,, are deposited.

2. Melt a few crystals of urea over a small flame and heat
gently for a minute, so that bubbles of gas arc slowly evolved.
Cool and add a few drops of water, then a drop of copper sul-
phate solution, and finally a few drops of caustic soda. A violet
or pink coloration is produced, depending upon the quantity of
biurct formed.

2CO(NHs)a = N

3. Add a few drops of sodium hypochlorite, or hypobromitc,
to a solution of urea in water. Nitrogen is given off,
CO(NH2)2 + 3NaOCl -"- N2-f-2lIaO H- 3NaCl + CO, (which
dissolves in the alkaline solution).